Conventional mechanical and electronic postage meters have heretofore secured the link between printing and accounting. The integrity of the physical meter box has been monitored by periodic inspections of the meters. Digital printing postage meters, which are closed system postage meters, typically include a digital printer coupled to a metering (accounting) device, which is referred to herein as a postal security device (PSD). Digital printing postage meters have removed the need for physical inspection by cryptographically securing the link between the accounting and printing mechanisms. In essence, new digital printing postage meters create a secure point to point communication link between the accounting unit and printhead. See, for example, U.S. Pat. No. 4,802,218, issued to Christopher B. Wright et al and now assigned to the assignee of the present invention. An example of such digital printing postage meters is the Personal Post Office manufactured by the Pitney Bowes Inc. of Stamford, Conn.
In even a modest size mailroom it is common that several meters are present. It has been shown that funds can be stored in one central location for batch mailing purposes where evidence of postage payment for batch mail printed at several printers is evidenced through the printing of a statement summarizing the postage for the batch of mail. See U.S. Pat. Nos. 4,760,532 and 4,837,701, each assigned to the assignee of the present invention. However, this scheme has limitations. For example, a malfunction at the central location can result in all of the meters becoming unusable, since they have no access to additional funds. In addition, in large mailrooms it is common for mail to be processed for several different originating zip codes. Since each meter is assigned one originating zip code, meters are frequently moved from one mailing machine to another depending upon the mail processing needs.